Many methods are known for forming the electrical interconnections between an integrated circuit and the supporting substrate. Tape automated bonding (TAB) is one commonly known method for forming these such electrical interconnections. A TAB tape is provided which comprises a plurality of individual long, slender inner leads attached to, and extending out from, generally wider, larger outer leads. There may be many of these inner/outer lead configurations on a single TAB tape.
An individual inner lead on the TAB tape is generally bonded to the integrated circuit at a bonding pad so as to form an inner lead bond. There are typically many of these inner lead bonds on a single integrated circuit. The inner lead bonds are formed by first depositing a gold bump, or other suitable material, on either the end of the TAB tape inner lead or on the integrated circuit itself. The integrated circuit and TAB tape inner leads, which are generally copper, are then aligned and simultaneously thermocompression gang bonded.
After bonding between the integrated circuit and inner leads is complete, the integrated circuit is excised from the TAB tape at a point beyond the outer lead, so that the outer lead remains attached to the bonded inner lead and integrated circuit. The integrated circuit assembly is subsequently mounted on the substrate, if this has not already been done, and the outer leads are appropriately bonded to the substrate.
Strain relief must be provided in the interconnection lead between the integrated circuit and supporting substrate, so as to compensate for any thermal or physical stresses arising during use. Generally strain relief is provided by forming the individual interconnection leads in a serpentine manner, as shown in the accompanying FIG. 1, thereby permitting expansion of the individual leads during use.
However, a shortcoming associated with the use of these individual serpentine leads is that the associated stresses become unbalanced during use due to the varying lead lengths and positioning of each lead from different directions. This unbalanced state results in higher failure rates for the individual bonds and correspondingly for the device. In addition, the current serpentine design results in increased lead stress during mounting of the integrated circuit to a substrate or other surface, since the varying lengths of each lead again result in an unbalanced stress load during mounting.
Therefore, it would be advantageous to provide an electrical interconnection lead which provides for balanced stress relief during use and mounting of the integrated circuit.